Laser materials processing as known in the art and used herein refers to performance of materials processes such as cutting, welding, drilling and soldering, using a continuous wave or pulsed laser beam. The average power of such a laser beam may range from as little as approximately one watt to 100's of watts, the specific power being selected on the basis of the particular process being performed. It is also known in the art to transmit the laser beam from the laser to the vicinity of the workpiece by means of a fiber optic. The apparatus and method for injecting a power laser beam into a fiber optic for transmission therethrough are disclosed in commonly assigned U.S. Pat. Nos. 4,564,736; 4,676,586; and 4,681,396 respectively entitled "Industrial Hand Held Laser Tool and Laser System", "Apparatus and Method for Performing Laser Material Processing Through a Fiber Optic", and "High Power Laser Energy Delivery System" the disclosures of those patents being incorporated in their entirety herein by reference.
In order to perform materials processing with the laser beam emitted at an output end of the transmitting fiber optic, it is necessary to terminate the fiber output end in an output coupler that includes lens apparatus for collimating and focusing the emitted beam. There are two major drawbacks to the use of such output couplers. The first drawback is that the physical sizes of the output coupler may prevent access to isolated or tightly spaced areas of the workpiece that require subjection to the materials processing laser. It would therefore be desirable to provide laser materials processing apparatus in which the output end of the beam transmitting fiber optic can be positioned to access isolated or tightly spaced areas of the workpiece.
The second drawback to the use of known fiber optic output couplers is that the coupler physical size prevents assembling a closely packed grouping of multiple fibers to accommodate a corresponding set of closely packed points on the workpiece, e.g. terminals of an electrical circuit component being soldered to a circuit board. It would therefore be desirable to provide laser materials processing apparatus in which the fiber optic output ends can be assembled into a closely packed group to accommodate a like group of points on the workpiece.
One attempted solution known in the art for overcoming the above described problems deriving from the output coupler size is the use of miniature lenses to construct the output coupler. Such miniature lenses typically have diameters that are two to five times the fiber diameter and are both difficult and expensive to fabricate. Further, it is especially difficult to fabricate such lenses with a focal length sufficient to maintain a reasonable working distance from the workpiece. Additionally, where the diameter of such miniature lenses is on the order of 1 mm, the aperture of the lens holding device may, disadvantageously, occlude a portion of the beam being collimated and focused thereby.
A second attempted solution known in the art to overcome the above described output coupler problems is to shape the output end of the fiber optic to control the shape of the emitted laser beam. If shaping of the emitted beam were successfully achieved by this method, then no lens would be required to collimate or focus the emitted beam. Typically, the fiber output end is shaped with a flame or CO.sub.2 laser beam to achieve a spherical shape. The spherical shape has a focusing effect with a focal point very close, e.g. less than 1 mm, to the end of the fiber. As a result, it is necessary to position the fiber end within 1 mm of the workpiece. Such proximity to the point of processing on the workpiece results in damage to the fiber end for most types of material processing.